Gymnodinium is a genus of dinoflagellates, a type of marine plankton. It is one of the few naked dinoflagellates, or species lacking armor (cellulosic plates). Since 2000, the species which had been considered to be part of Gymnodinium have been divided into several genera, based on the nature of the apical groove and partial LSU rDNA sequence data.[2] Amphidinium was redefined later.[3][4] Gymnodinium belong to red dinoflagellates that, in concentration, can cause red tides.[5]

^Daugbjerg, N.; Hansen, G.; Larsen, J.; Moestrup, Ø. (2000). "Phylogeny of some of the major genera of dinoflagellates based on ultrastructure and partial LSU rDNA sequence data, including the erection of three new genera of unarmoured dinoflagellates". Phycologia. 39 (4): 302–317. doi:10.2216/i0031-8884-39-4-302.1.